A mobile telephone, a digital camera, or the like includes a display device, and the display device is configured by, for example, a liquid crystal panel. Such a display device displays information by utilizing emitted light. Under the circumstances, there have been demands to control an amount of emitted light based on an illuminance of the emitted light which has been measured by an illuminance sensor. For example, there have been demands as follows: that is, in a case where a liquid crystal panel is used as the display device, an amount of light emitted by a backlight of the liquid crystal panel is optimally controlled so as to improve display image quality and/or to reduce power consumption.
Moreover, in a case of a mobile terminal such as a mobile telephone or a smart phone, it is preferable to turn off a display device while it is unnecessary to view the display device (e.g., while talking on the terminal), in view of reduction in power consumption. In order to judge such a case, there has been a demand to detect approach of a face of a user, who is using the mobile terminal, to the mobile terminal by a proximity sensor.
Moreover, there has been a demand to reduce a size of a mobile terminal, and recently, a small single-unit illuminance/proximity sensor has been proposed which serves as both an illuminance sensor and a proximity sensor.
Here, the illuminance sensor is required to have a spectral characteristic near to luminous efficacy. The spectral characteristic near to luminous efficacy means a spectral characteristic which has a sensitivity mainly in a visible light region. That is, it is preferable that an infrared component can be removed from light which is to be received by the illuminance sensor. Meanwhile, the proximity sensor detects proximity by utilizing infrared light, and it is therefore preferable that an infrared component is selectively contained in light which is to be received by the proximity sensor.
As such, in order to realize a single-unit illuminance/proximity sensor, it is necessary to achieve both the conflicting functions, i.e., removal and utilization of an infrared component.
Patent Literature 1 discloses a semiconductor light sensor which includes, in order to achieve a spectral characteristic near to luminous efficacy in an illuminance sensor, (i) a first amplifier circuit which amplifies a photoelectric current supplied from a first photodiode, (ii) a second amplifier circuit which amplifies a photoelectric current supplied from a second photodiode and has an amplifying characteristic that is substantially identical with that of the first amplifier circuit, and (iii) an infrared transmissive filter which is provided on the second photodiode and attenuates, relative to an infrared light component, a visible light component in incoming light. In the semiconductor light sensor, a difference between an output of the first amplifier circuit and an output of the second amplifier circuit is outputted by a subtracting circuit.
In order to provide an illuminance sensor for which an infrared component is removed from incoming light, a difference between outputs of a plurality of photodiodes, which have different spectral characteristics, is generally obtained as in the configuration disclosed in Patent Literature 1.
FIG. 16 is a schematic view illustrating a configuration of a sensor 100 in accordance with a conventional technique disclosed in Patent Literature 1. As illustrated in FIG. 16, the sensor 100 includes a light receiving element section E101, a light receiving element section E102, and an infrared transmissive filter IRthrF which attenuates, relative to an infrared light component, a visible light component from incoming light toward the light receiving element section E102. Here, the light receiving element sections are configured by respective photodiodes having different spectral characteristics. Moreover, the light receiving element section E102 is provided with the infrared transmissive filter IRthrF, and outputs an electric current, which corresponds to the infrared component in the incoming light, by attenuating the visible light component from the incoming light relative to the infrared component. Then, from an electric current outputted by the light receiving element section E101, an electric current outputted by the light receiving element section E102 is subtracted, and thus influence of infrared light is eliminated and a spectral characteristic corresponding to luminous efficacy is obtained.
Patent Literature 2 discloses a light receiving element which includes (i) a first semiconductor layer having a first conductivity type, (ii) a second semiconductor layer which is embedded in a surface layer part of the first semiconductor layer and has a second conductivity type different from the first conductivity type, (iii) a third semiconductor layer which is embedded in a surface layer part of the second semiconductor layer and has the first conductivity type, and (iv) a wire via which the second semiconductor layer and the third semiconductor layer are connected with each other. That is, Patent Literature 2 discloses a configuration in which light receiving elements are used which are arranged at different junction depths.
FIG. 17 is a schematic view illustrating a configuration of a light receiving element section 200 in accordance with a conventional technique disclosed in Patent Literature 2. As illustrated in FIG. 17, the light receiving element section 200 includes a first photodiode PD1 and a second photodiode PD2 which is provided at a location shallower than that of the first photodiode PD1. Further, the second photodiode PD2 is short-circuited by a wire 201. With the configuration, an electric current, which corresponds to light that has entered the second photodiode, will not be outputted. That is, according to the light receiving element section 200, a spectral characteristic becomes near to luminous efficacy in a short wavelength region, and an electric current I corresponding to the spectral characteristic is outputted via the wire 202.
Patent Literature 3 discloses a proximity illuminance sensor which includes (i) a light-emitting element, (ii) an illuminance sensor light receiving element, (iii) a distance detecting light receiving element, (iv) a first visible light resin which molds to the illuminance sensor light receiving element, and (v) an infrared cut filter which is provided so as to cover an entire surface of the first visible light resin which surface is opposite to a surface that makes contact with the substrate.
FIG. 18 is a schematic view illustrating a configuration of a sensor 300 in accordance with a conventional technique disclosed in Patent Literature 3. According to the sensor 300 illustrated in FIG. 18, an illuminance sensor light receiving element E301 and a proximity sensor light receiving element E302 are embedded in a resin sealing part 301. Here, on a surface of the resin sealing part 301, a lens shape 302 can be molded.
An infrared cut-off filter IRcutF is provided on an upper surface of the resin sealing part, and therefore the illuminance sensor light receiving element E301 selectively receives visible light, and a spectral characteristic becomes near to luminous efficacy. Moreover, the proximity sensor light receiving element E302 receives infrared light which has been reflected from a proximity detectable object and has passed through the resin sealing part 301.
The following description will discuss a general proximity sensor with reference to FIG. 19 and FIG. 20.
FIG. 19 is schematic view illustrating a configuration of a general proximity sensor in accordance with a conventional technique. The proximity sensor illustrated in FIG. 19 includes a light emitting diode LED, a photodiode PD, and a control circuit. The control circuit supplies a pulsed current to the light emitting diode LED so as to drive the light emitting diode LED. Thus, the light emitting diode LED emits pulsed light. In a case where a proximity detectable object exists in the vicinity of the proximity sensor, pulsed light emitted by the light emitting diode LED is reflected by the proximity detectable object as indicated by the solid arrow and is then received by the photodiode PD. On the other hand, in a case where no detectable object exists, the pulsed light emitted by the light emitting diode LED is not reflected by a detectable object as indicated by the dotted arrow, and therefore the pulsed light from the light emitting diode LED hardly reaches the photodiode PD.
The photodiode PD converts received light into an electric current, and outputs the electric current to the control circuit. The control circuit judges, based on a magnitude of the electric current supplied from the photodiode PD, whether or not a proximity detectable object exists in the vicinity of the proximity sensor.
FIG. 20 is a waveform chart illustrating each case where proximity/non-proximity of a proximity detectable object is detected by the proximity sensor of the conventional technique. (a) of FIG. 20 illustrates a case where proximity of a detectable object is detected, and (b) of FIG. 20 illustrates a case where non-proximity of a detectable object is detected. Assuming that a digital signal Dout in a time period during which the light emitting diode LED is driven is Data 1 and a digital signal Dout in a time period during which the light emitting diode LED is not driven is Data 2, a difference between Data 1 and Data 2 (i.e., Data 1−Data 2) becomes proximity data.
As illustrated in (a) of FIG. 20, in a case where the light emitting diode LED is driven when a proximity detectable object exists, reflected light from the proximity detectable object is strong, and accordingly an electric current flowing in the photodiode PD is high. From this, the proximity data (Data 1−Data 2) becomes greater than a threshold Data_th of the control circuit, and thus proximity is determined.
On the other hand, as illustrated in (b) of FIG. 20, in a case where the light emitting diode LED is driven when no proximity detectable object exists, incoming light toward the photodiode PD is weak, and accordingly an electric current flowing in the photodiode PD is low. From this, the proximity data (Data 1−Data 2) does not become greater than the threshold Data_th of the control circuit, and thus non-proximity is determined.